Cellular digital packet data mobile data base station

ABSTRACT

A cellular digital packet data (CDPD) system includes a mobile data base station (MDBS) configured to interface easily with an advanced mobile phone system (AMPS). The elements of the MDBS are arranged on modules and the functionality of the MDBS is divided among the modules to facilitate flexibility, compactness and quick expansion of the MDBS. To further facilitate compactness, the MDBS includes a transceiver/modem board which uses a single chip to carry out delta-sigma modulation. In order to maintain the integrity of CDPD transmission, a channel hopping scheme is used based upon avoidance of AMPS channel use. A distinctive protocol is used to encapsulate control/query/response data for transmission throughout the CDPD system. This protocol also facilitates easy control of each MDBS throughout the system.

This application is a continuation of U.S. application Ser. No.08/152,005, now U.S. Pat. 5,544,222, and is also related to U.S. patentapplication Ser. No. 08/461,618.

This application is related to and incorporates by reference U.S. patentapplication Ser. No. 08/117,913, filed Sep. 8, 1993, and U.S. patentapplication Ser. No. 08/150,728 filed Nov. 12, 1993, entitled "METHODAND APPARATUS FOR SWITCHING BETWEEN RADIO FREQUENCY CIRCUITS" (AttorneyDocket No. 2167-003). This application incorporates by reference both ofthese applications.

TECHNICAL FIELD

This invention relates generally to wireless communication systems. Moreparticularly, the invention relates to cellular base stations supportingtransmission and reception of data, fax, and voice signals.

BACKGROUND OF THE INVENTION

Mobile wireless communication of analog voice signals was initiallycarried by half duplex radio systems. Citizens Band radio, one type ofmobile wireless radio, uses amplitude modulation (AM) upon a carrierfrequency to transmit or receive voice signals in a half duplex manner.Other mobile wireless radios used frequency modulation (FM) within agiven carrier frequency range in order to transmit or receive voicesignals, half duplex, achieving improved noise characteristics. Thesemobile wireless radios allowed a user to move within a given radius ofantennas.

A disadvantage attributable to these systems was that once a user wasbeyond a certain range of a given base antenna, the radio channel for agiven carrier frequency was inoperative. Another disadvantage was thatwireless half duplex voice communication was unacceptable to mostconsumers. The consumer wanted a wireless duplex voice communicationsystem similar to his or her wired home telephone.

In the 1980's, mobile wireless duplex voice communication using ananalog FM based cellular radio was introduced into the marketplace. Thisanalog cellular system for mobile wireless duplex voice transmission wascalled "Advanced Mobile Phone Service" (AMPS). Introduced by AT&T, theAMPS cellular network uses the FCC assigned carrier frequency range of800 to 900 MHz. AMPS automobile cellular units were first permanentlyattached to the user's car. Automobile cellular units transmitted voicesignals to a cellular base station within a given cell using one watt ofpower. Hand-held cellular units using battery power supplies were laterintroduced and transmitted voice signals to a cellular base stationwithin a given cell using one quarter watt of transmit power. Becausehand held cellular units operated from a battery power supply, the powerconsumed by the cellular phones became critical. When a cellular phoneis powered on and waiting to receive a phone call, it is in a stand-bymode consuming less power than in an active mode. However, when the handheld unit is in a stand-by mode, it constantly listens for itsregistration number in order to become active and receive a phone call.The stand-by mode, although lower in power than the active communicationmode, continuously uses a considerable amount of power. It is desirableto further decrease the amount of power used in the stand-by mode inorder to further increase the time the cellular unit requires forrecharging or replacing batteries.

The human analog voice was the signal that the AMPS system was firstdesigned to communicate. The AMPS system was optimized for carrying asmany analog voice signals within a given bandwidth of a channel aspossible. Mobility of the cellular telephone using low power mobileunits, FM modulation, and the higher carrier frequency range (800MHz-900 MHz) is achieved through a cellular arrangement of antennaswhereby a user's signal is handed off to the next cell site as he or shemoves into a different cell area. This cellular handoff can cause atemporary loss in transmission or reception. However, temporarily losinga voice signal is not critical because a user knows when there is asignal loss and can retransmit the voice information. However, signalloss, even though temporary, poses special problems for transmission ofdigital data. Some other AMPS mobile cellular problems causing a loss ina voice signal are fading signal strength, reflections, Rayleigh fading,and cellular dead spots.

The availability of portable computers naturally led to the desire totransmit digital data via wireless from a remote location. Presently,the AMPS voice cellular system is being used to transmit digital data inthe form of Circuit Switched Cellular Data across AMPS carrier channels.Raw (baseband) digital data is converted so that it can be transmittedand received across the analog AMPS system. One disadvantage to usingthe AMPS system is that a narrow channel bandwidth and errors intransmission limit the baud rate of transmitting and receiving digitaldata. Another disadvantage of using AMPS to communicate digital data isthat movement of the subscriber unit may cause a cellular handoff tooccur, thus causing a loss of the digitally transmitted or receivedinformation. Loss of digital data may corrupt a data file such that itis useless. Other losses of the raw digital data may be caused by otherproblems of the AMPS mobile cellular system.

Another wireless communication device is a pager. Most pagers usesimplex or one way communication receiving only a limited amount ofinformation such as a telephone number. Most pagers display onlyinformation to a user on demand and perform no other function. Becauseonly one way communication is required, an acknowledgement is notreturned by the pager to the original sender. In many cases it isdesirable that a sending party receive an acknowledgement minimally,telling him or her that their page message was received. In some casesit may be appropriate to respond by leaving a return page message.

A disadvantage of present paging systems is that acknowledgment andreturn pages are not widely available because simplex paging is morecommercialized than other paging modes. Another disadvantage of presentpagers is that a displayed telephone number is not automatically andelectronically dialed directly on a telephone. A user reads thetelephone number from a pager's display and manually dials the number ona telephone in order to contact the paging party. It is desirable for awireless pager to have the capability of automatically dialing areceived telephone number on a wireless cellular telephone viaelectronic means, thus integrating the features of a wireless cellulartelephone with that of a duplex pager.

A landline-dependent system that is presently widely used is a highspeed fax-modem. Fax-modem hardware and firmware in conjunction with faxand data communication application software have the capability ofsending digital data over various modem protocols as well as sendingfacsimile data by using the various facsimile protocols. Fax or datacommunication application software may operate on different hardwaresuch as home or portable computer, personal communicator, personaldigital assistant, or other electronic devices. Examples of modemprotocols for standard modulated data are CCITT V. 22bis, CCITT V. 23,CCITT V.32, Be11103, and Be11212A. Modem protocols that include errorcontrol include CCITT V.42, MNP2, MNP3, MNP4, and MNP10. Modem protocolsthat provide data compression are CCITT V. 42bis and MNP5. Facsimileprotocols include CCITT V.21, CCITT V.27ter, CCITT V.29, CCITT T.4,CCITT T.30, CCITT T.35, Class I-EIA/TIA 578, Class I-EIA 592, and ClassII-EIA 578-SP2188. A fax-modem accepts raw (baseband) digital data froman electronic device over an internal data bus or external RS-232 port.Raw digital data is converted and modulated into data of a givenprotocol for transmission onto a standard telephone line. Data receivedfrom the telephone line can be converted from the modulated form intoraw digital data that can be interpreted by the hardware, firmware andapplication software.

A disadvantage of present fax-modems is that most require a wireconnection to a telephone line. Present methods of providing wirelesscapability for a fax-modem take the modulated analog modem output signalfrom a fax-modem and input this into an AMPS conversion unit. The AMPSconversion unit converts and modulates the transmitted analog modemoutput signal into a different analog form for transmission onto theAMPS network The analog modem output signal is converted into what iscalled Circuit Switched Cellular Data. Received AMPS signals can beconverted from Circuit Switched Cellular Data by the AMPS conversionunit into analog modem input signals that the fax-modem can receive.Presently, fax-modems do not directly convert and modulate raw digitaldata into an analog signal for transmission onto the AMPS cellularnetwork. A disadvantage of present methods of providing wirelessfax-modem capability is that they require additional devices to send orreceive fax and digital data over the AMPS cellular network. Anotherdisadvantage is that more power is necessary for additional components,such as the AMPS conversion unit. Another disadvantage is that a usermust carry the portable computer, fax-modem, and AMPS conversion unit toprovide wireless fax-modem capability. It is desirable to incorporate afax-modem and AMPS conversion unit into one unit providing thecapability of sending Circuit Switched Cellular Data across the AMPSnetwork.

A disadvantage of using Circuit Switched Cellular Data communicationacross an AMPS system is the requirement of the mobile unit to bestationary to avoid losing data from fading or cellular handoffassociated with a non-stationary mobile AMPS communication. Thus, amobile unit should avoid being moved even slightly when performingcommunication of Circuit Switched Cellular Data using the AMPS network.

Heretofore, providing efficient wireless transmission of both voice anddata signals into one small hand held integrated package has beendifficult. Furthermore, it is difficult to integrate the features ofAMPS voice transmission with applications such as data transmission,electronic mail, duplex paging, as well as the provision of a CircuitSwitched Cellular Data interface such as a wireless fax-modem, into asingle hand held battery operated wireless unit. Further, theintegration of these features into a single hand held unit has not beenpossible because of the unavailability of the underlying electroniccomponents and application software required to integrate all thesefeatures into a single hand held unit. It is desirable to integrate AMPSvoice communication and a data communication mode when moving betweencell sites, as well as providing the capability of Circuit SwitchedCellular Data Communication into one integrated hand-held unit. It isalso desirable to provide a system supporting such communication tointerface easily with existing AMPS systems.

BRIEF SUMMARY OF THE INVENTION

object of the present invention is to facilitate the use of a cellulardigital packet data (CDPD) mobile data base station with existingadvanced cellular (AMPS) facilities.

A further object of the present invention is to use AMPS communicationchannels for CDPD communication in a manner entirely transparent to theAMPS system.

Still a further object of the present invention is to share front endequipment such as antennas, duplexers, and amplifiers with existing AMPSsystems in a manner non-intrusive upon the operation of that AMPSsystem.

An additional object of the present invention is to reduce the size ofthe elements necessary for a CDPD mobile data base station.

Another object of the present invention is to program the mobile database stations of a CDPD system using a protocol flexible for a varietyof different types of communication.

Yet another object of the present invention is to provide modificationsand expansion of the MDBS without impacting the associated AMPS system.

The aforementioned objects are carried out by a mobile data base stationconfigured to transfer cellular digital packet data between a mobilesubscriber and an external communication network. The mobile data basestation includes a controller board operatively connected to theexternal communication network via a data link and a transceiver boardproviding a radio link to a mobile subscriber. The transceiver board isseparate and distinct from the controller board.

Another aspect of the present invention is a method for conveying datafrom a network management system to a mobile data base station. Themethod includes the steps of encoding instruction data according to apredetermined MDBS utility protocol (MUP). The instruction data isfurther encoded according to a second protocol and then transferred overa DS0 line. The twice-encoded data is received at least at one MDBS anddecoded according to both protocols so that the instructions can becarried out at the MDBS.

An additional aspect of the present invention is a method of operating aCDPD system having at least one mobile data base station associated withan AMPS system and connected via radio frequency link to a mobile endstation. The method includes the steps of detecting at the MDBS all AMPScommunications on all radio frequency channels associated with that AMPSsystem. From this data a list of channels is derived based upon AMPSuse. The MDBS then sends the list of channels to any mobile end systemwithin range of the MDBS. Each of the mobile end systems receiving thelisted data then selects channels for CDPD use based upon theinformation in the list.

A further aspect of the present invention is a CDPD system associatedwith an AMPS system having at least one mobile data base station wherethe MDBS includes means for detecting AMPS communications on radiofrequency channels encompassed within the AMPS system. The MDBS alsoincludes means for deriving a list based upon AMPS use of the radiofrequencies and means for periodically adjusting that list in responseto AMPS use. The MDBS further includes means for sending data regardingthe list to mobile end systems within range of the MDBS.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a CDPD system.

FIG. 2 is a block diagram comparing a CDPD system to an AMPS system.

FIG. 3 is a perspective drawing of a chassis containing a mobile database station.

FIG. 4 is a block diagram of the overall MDBS architecture.

FIG. 5 is a block diagram showing the interconnections between the MDBSand shared AMPS front end equipment.

FIG. 6 is a block diagram of the architecture of theSniffer/modem/transceiver board (SNODEM).

FIG. 7 is a block diagram showing the functional elements in adelta-sigma modulator contained on the SNODEM board.

FIG. 8 is a block diagram of the control computer architecture.

FIG. 9 is a block diagram/flow chart of protocols carried out in theCDPD communication process and correlation of that protocol to elementsin the MDBS.

FIG. 10 is a block diagram illustrating connections between a mobiledata base station and a network controller sending instruction data tothat MDBS.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One solution to the aforementioned difficulties of integrating portablevoice and data communications resides in a new digital wirelesscommunication technology developed to overcome some of the undesirableeffects of transmitting raw digital data over the AMPS system. This newdigital wireless communication system and network is called CellularDigital Packet Data (CDPD). The CDPD communication system shares thesame carrier frequencies assigned to standard AMPS channels andstandards.

The base unit, mobile data base station (MDBS 1, as illustrated in FIG.1), of the preferred CDPD system (MAV) utilize an channel within an AMPScell to establish a link and communicate to a user's mobile end system.The MDBS may be applicable to other frequencies outside of AMPS thatopen up to it. The mobile end system (M-ES 2) is a portable computer,handset or other portable electronic device containing a subscribercommunication unit. The MDBS serves as a communication link between theuser of the M-ES 2 and a service provider's network of wire lines,microwave links, satellite links, AMPS cellular links, or other CDPDlinks (such as mobile data intermediate system MD-IS 3, intermediatesystems 4, 5, 6) to convey data to another mobile end system, computernetwork, or non-mobile or fixed end-user system (F-ES 7, 8).

The CDPD network is designed to operate as an extension of existingcommunication networks, such as AMPS networks and the internet network.From the mobile subscriber's perspective, the CDPD network is simply awireless mobile extension of traditional networks. The CDPD networkshares the transmission facilities of existing AMPS networks andprovides a non-intrusive, packet-switched data service that does notimpact AMPS service. In effect, the CDPD network is entirely transparentto the AMPS network, which is "unaware" of the CDPD function.

The CDPD system employs connectionless network services (CLNS) in whichthe network routes each data packet individually, based on thedestination address carried in the packet and knowledge of currentnetwork topology. The packetized nature of the data transmissions from amobile end system 2 allows many CDPD users to share a common channel,accessing the channel only when they have data to send and otherwiseleaving it available to other CDPD users. The multiple access nature ofthe system makes it possible to provide substantial CDPD coverage tomany users simultaneously with the installation of only one CDPD stationin a given sector (transmitting range and area of a standard AMPS basestation transceiver).

The airlink interface portion of the CDPD network consists of a set ofcells. A cell is defined by the geographical boundaries within the RFtransmission range from a fixed transmission site such as MDBS 1, whichcan be received at acceptable levels of signal strength by mobilesubscribers such as M-ES 2. The transmitter supporting the cell may belocated centrally within the cell, with transmission carried out via anomni-directional antenna, or the transmitter may be located at the edgeof a cell and transmitted via a directional antenna. This second type ofcell is also referred to as a sector. In typical configurations, thetransmitters for several sectors are co-located. The area served by aset of cells have some area overlap, so that a roaming mobile end systemcan maintain continuous service by switching from one cell to anadjacent cell in a manner roughly analogous to the standard hand-off inan AMPS system. The two cells are considered to be adjacent if an M-EScan maintain continuous service by switching from one cell to the other.This switching process is called cell transfer, and is doneindependently of normal AMPS hand-off procedures.

In FIG. 1, the interface (A) between the mobile end system 2 and theMDBS 1 is an "air interface" constituted by a radio frequency link usingstandard AMPS frequencies. The MDBS 1 is connected to other mobile database stations through a mobile data intermediate system (MD-IS) 3. Anumber of mobile data base stations can be under the control of a singlemobile data intermediate system. The mobile data intermediate systemsare connected to each other through intermediate systems such as 4 and 5in FIG. 1.

The intermediate systems are constituted by at least one node connectedto more than one sub-network (such as an MD-IS). The intermediate systemhas a primary role of forwarding data from one sub-network to another.The mobile data intermediate system 3 performs data packet routing basedon knowledge of the current location of each mobile end system withinthe range of the mobile data base stations under the control of theMD-IS. The MD-IS is the only network entity that is "aware" of thelocation of any of the mobile end systems. A CDPD-specific MobileNetwork Location Protocol (MNLP) is operated between each MD-IS (throughthe intermediate system) to exchange location information regarding themobile end systems.

The overall CDPD network is controlled by a network management system(NMS) 10 having an interface with at least one mobile data intermediatesystem 3. Using a special protocol, programming instructions can betransmitted from the NMS 10 through the MD-IS 3 to any number of mobiledata base stations under the proper conditions.

Such programming instructions can be used to convey useful network datato the MDBS, as well as configuring the operation of an MDBS withrespect to such critical features as maintaining channel queues. The NMSalso controls other CDPD system characteristics such as the timing ofpaging messages to coincide with the non-dormant periods of the M-EShand-sets. One advantage of the present invention is the capability ofproviding operating instructions to mobile data base stations from theNMS 10 through an MD-IS 3, or by a direct connection to the MDBS as isoutlined in the detailed description of the MDBS architecture. Thefunctions and protocol as carried out by each of the mobile end systemsand the mobile data base station are explained in greater detail laterherein.

FIG. 2 provides a comparison between the CDPD network illustrated inFIG. 1 and the standard AMPS network. The MDBS 1 is the CDPD equivalentto an AMPS base station 21. Both serve as links to mobile users, 2, 2',and 2" for the CDPD system and 22, 22' and 22" for AMPS users. Aspreviously indicated in U.S. Pat. application Ser. No. 08/117,913, filedSep. 8, 1993, both AMPS and CDPD functions are preferably handled by thesame hand-set or end system equipment. Also, the MDBS 1 is preferablylocated with the AMPS base station 21 as be will explained in greaterdetail later.

The mobile data intermediate system 3 which acts as a local controllerfor the mobile data base stations connected thereto is equivalent to themobile telephone switch office (MTSO) 23 used to control a plurality ofAMPS base stations 21, 21' and 21". In the AMPS system, the MTSO 23 canbe connected to the various base stations 21, 21', 21" by way ofcommunication links, either over dedicated land-lines or through apublic switched telephone network (PSTN). Likewise, the connectionbetween MD-IS 3 and the various mobile data base stations 1, 1', 1"controlled thereby is made in the same manner. However, differentsignaling protocols are used than those found in the AMPS system.

In comparison to AMPS, the infra-structure requirements of CDPD are verysmall. The CDPD base station equipment is located (preferably) at acellular carrier's cell site along side existing AMPS base stationcellular equipment. The multiple access nature of the CDPD system makesit possible to provide substantial CDPD coverage to many userssimultaneously with the installation of only one CDPD radio in a givensector. This multiple access is the result of a mobile end-systemaccessing the CDPD channel only when there is data to be sent.

The AMPS base station and the MDBS can use the same RF links if both areco-located. (In contrast, the MTSO of the AMPS system and the MD-IS ofthe CDPD system do not have to be co-located in order to share RFlinks.) In the AMPS system, the MTS0 23 has the responsibility ofconnecting the AMPS base station and the mobile station to another party28 through a public switched telephone network 24 (PSTN). Theintermediate system 4 of the CDPD corresponds to the use of the PSTN bythe AMPS system. Like the AMPS system, the CDPD system must also use thepublic switch telephone network or another landline network forcompleting calls to remote parties or systems such as 28. However, theCDPD system employs a different protocol than that used by the AMPSsystem for completing calls over a PSTN.

In general, the CDPD system illustrated in FIG. 1 operates to provideservice to manage data communications to subscribers over a widegeographic range. When a mobile end system is located in its home area,data packets are routed directly to and from it by the home MD-IS viathe home MDBS. The route via which data packets are forwarded to andfrom a mobile end system changes when the mobile end system roams out ofits home area.

The CDPD system operates to provide a mobile home function (MHF),including a fixed reference location for each M-ES, where each M-ES isassociated with a specific MDBS which is located in a fixed home area,and which keeps track of the location of the M-ES when it roams out ofits home area. The MHF consists of two services: location directoryservice, maintaining an information base of the current serving area foreach of the M-ES listed in the system; and a redirection and forwardingservice, operating in a forward direction (from caller to mobilesubscriber) only. The packeting forwarding service of the mobile homefunction routes packets destined for a roaming M-ES. In the forwarddirection (packets destined for an M-ES), packets are routed first tothe MD-IS in the home area, then encapsulated and tunneled to the MD-ISin the current serving area. The packets are then routed to the calledM-ES at its current cell location through the MDBS serving that cell. Inthe reverse direction (originating from an M-ES), packets are routeddirectly to their destination. There is no requirement for packetstraveling in the reverse direction to carry the home MD-ISidentification.

The MDBS maintains zero or more (up to the MDBS transmission capability)channel streams across the airlink interface, as directed by the MD-IScontrolling that MDBS. The MDBS instructs all subscriber units to changechannels when necessary such as when an AMPS communication is detectedon the CDPD channel. Each subscriber unit's terminal stream is carriedon one channel stream at a time, normally selected by the mobilesubscriber, preferably based upon data received from the MDBS regardingoptimum channels for CDPD use. The forward and reverse traffic in agiven cell (its terminal stream) is carried on a single DS0 trunk,between the MDBS and the MD-IS. The communication between the MDBS andthe MD-IS over the DS0 trunk follows standard formats such as T1.

Within the CDPD network, digital data is burst mode transmitted betweena given subscriber unit (SU) within a mobile system and a mobile database station (MDBS) using Gaussian Minimum Shift Keying (GMSK)modulation. Communicating in a burst mode fashion reduces the time thatan SU communicates with an MDBS such that other SUs can talk with thesame MDBS. For a given data size, the CDPD connect time is reducedconsiderably when compared to sending digital data over the AMPSnetwork. Presently the raw (baseband) digital data envisioned beingtransferred across CDPD are electronic mail messages, digital fax data,or digital data representing a network connection such that files may betransferred as if currently connected to a local area network. OtherCDPD applications are being developed such as CDPD duplex paging.

The MD-IS handles the routing of packets for all visiting mobile endsystems in its serving area. When a M-ES registers for network access inan MD-IS serving area, the home MD-IS is notified of the currentlocation of the subject M-ES. Two services are performed by the MD-IS: aregistration service maintaining an information base of each M-EScurrently registered in a particular serving location; and a re-addressservice, decapsulating forwarded packets and routing them to the correctcell. The serving MD-IS also administers authentication, authorizationand accounting services for the network support service applications.

Within a cell area the MDBS first performs "RF sniffing" in order todetect an unused AMPS channel. CDPD use of an AMPS channel is limited tothe idle time between AMPS channel access. If an AMPS cellular unitbegins transmitting on a channel occupied by CDPD, the CDPD unit ceasestransmitting on that channel and waits until the same channel becomesavailable or switches, referred to as channel hopping, to a differentavailable channel.

Although the CDPD system shares existing AMPS radio frequency channels,as stated above, AMPS calls are given first priority, and they arealways able to pre-empt the use of any channel being used by CDPD.However, the cellular service provider may opt to dedicate a channel orchannels to CDPD usage. In this case, AMPS calls will never attempt topre-empt the channels dedicated to CDPD use. It is noted that the use ofsuch dedicated channels undermines optimum usage of AMPS systems in thatthe dedicated channels are no longer available for AMPS usage.

Normally, the MDBS functions to monitor activity on AMPS channels. Basedupon this activity, a list or a series of list will be maintained at theMDBS to indicate those channels least likely to be used by the AMPSsystem and thus, most beneficial for possible CDPD use. This informationis passed to each M-ES within range of that base station. Thus, eachM-ES is provided with information as to which channel (out of all ofthose designated for CDPD use by the MDBS) will be selected in case thepresent CDPD channel is preempted by AMPS communication, as well as themost likely candidates for future channel hopping.

One aspect of normal CDPD systems is that CDPD communication isinterrupted upon detection of an AMPS communication on the CDPD channel.Such interruption entails the loss of data with the consequentrequirement that the lost data be retransmitted when another CDPDcommunication can be arranged via the MDBS. Also, once CDPDcommunication is pre-empted, the mobile subscriber must hunt for anotherchannel available for CDPD communication, creating further delay. Thesituation can be avoided if AMPS usage can be predicted and channelhopping arranged to periodically select channels for optimal CDPD usage,and carrying out the channel hopping between data transmissions.

The base station described infra. is configured to carry out theaforementioned functions in the most efficient manner practical. Thebase station monitors all AMPS communications, derives a list (queue) ofchannels most likely to be selected for AMPS usage, and then derives asecond list of channels most likely to be good candidates for CDPD usagebased upon AMPS usage. This data is transmitted to each of the mobileend systems within the sector of the MDBS. Predicted channel hops aredetermined by the MDBS, and the channel to hop to is broadcast in a"switch channels message" to the subscriber units. A properly programmedsubscriber unit will stop transmitting after getting a "switch channelsmessage" and retransmit the data after acquiring the new channel. Themobile subscribers use the channel data broadcast from the MDBS to guidethem in their search for a new channel after the channel hop hasoccurred. More particular procedures for deriving lists for optimum CDPDuse are explained in greater detail, infra.

The CDPD system has the capability of easily interfacing with existingAMPS systems and sharing some front-end equipment with the existing AMPSsystem. To take advantage of this capability the MDBS must have thecapability of physically interfacing with existing AMPS base stations.Consequently, the MDBS should be small, non-obtrusive, and easilyaccessible without interrupting existing AMPS equipment. The MDBS has tobe configured so as to easily be connectable to equipment outside of theMDBS which is normally shared with the AMPS system. Thus, the MDBS mustbe easily connectable to the following pieces of external equipmentfound in the AMPS base station: an antenna system; RF power amplifiers(in particular, linear amplifiers can be shared with existing AMPS), RFmulticouplers; power splitters; duplexers; and, optional equipment.Since the MDBS shares the environment of the AMPS base station, the MDBSshould not constitute a substantial additional burden upon such supportsystems as environmental control and maintenance. Thus, the MDBS must becompact and flexible, constituting only those elements necessary forcarrying out the MDBS functions necessary at that cell site.

In order to maximize compactness and modularity, the MDBS is arranged asshown in FIG. 3. A casing 30 is provided with angle hardware 35 used formounting to vertical supports 36 arranged within the AMPS base station.Using this arrangement, the casing can be mounted at any height from thefloor or ceiling within the AMPS base station structure. The flexibilityis provided by the modular arrangement of the MDBS by which thefunctions of the MDBS are divided and arranged on separate boardsslidably mounted within casing 30. Typical measurements for the size ofthe housing 30 are shown in FIG. 3. With this size housing, twocontrolled computer boards 31, 6 SNODEM boards 32 and two powerconverter boards 33 can be accommodated. However, casing 30 can befabricated to accommodate more boards than shown in FIG. 3. Also, morethan one such casing can be associated with an AMPS base station.

Whatever the size of the casing 30, the MDBS requires at least onecontrol computer board 31, one power converter board 33, and at leastone SNODEM board 32. However, even in a minimal arrangement two SNODEMboards 32 are considered preferable. The casing 30 is arranged toaccommodate at least one DS0 connection (from the control computer board31). The casing 30 also is arranged to accommodate connections to theaforementioned front-end equipment which is installed as part of thenormal AMPS base station. In the alternative, the MDBS need not sharethe existing AMPS base station front-end equipment, and can use afront-end system dedicated solely to CDPD use. Casing 30 can be expandedto accommodate this dedicated front-end equipment.

As illustrated in FIG. 3, each board is slidably mounted within thecasing 30, and can be withdrawn as shown. The boards are secured inplace by standard hardware to prevent vibration and loose connections.The presence or absence of any particular board is detected by circuitry(not shown) connected to contacts connecting the board to the backplane.Each of the contacts between the boards and the backplane are designedwith an impedance suitable to allow insertion and removal of the boardswithout arcing of power surges. This technique is.

The connections between the various boards illustrated in FIG. 3 arefacilitated by backplane structure 42 in FIG. 4. The backplane isconstituted by a serial bus and is used to connect the control boards 44and 44' to the various transceiver boards 45. The power board (33 inFIG. 3) is also connected to the rest of the system through thebackplane 42. Each of the control computer boards 44, 44' is connectedto the MD-IS 3 (in FIG. 1) through a DS0 trunk. The forward and reversetraffic of a given subscriber unit (its terminal stream) is carried on asingle DS0 trunk between the MDBS and the MD-IS. It is the function ofthe MD-IS to reassign all subscriber units supported on a given DS0trunk before deactivating that trunk.

As indicated in FIG. 4, a fully populated MDBS transceiver bank consistsof two control computers 44, 44', six Sniffer/modem/transceiver boards45 and two power supply boards (not shown). The second power supplyboard is necessary for redundancy, and serves as an aid in faultdetection in a manner well known in the power supply art. Such a systemcan transmit and receive on up to six channels simultaneously. The sixchannels can be allotted to sectors in any fashion desired; for example,six CDPD channel pairs for an omni-directional site or two channels persector for a three-sector site. The allocation can be changed by meansof instructions received over the DS0 trunk by a control computer boardin the MDBS. Normally, such instructions are sent from the NMS 10 (inFIG. 1). However, they can also be input locally using a utility port.

Channel capacity can be expanded by adding up to nine chassis (with afull complement of SNODEM boards), yielding a total of 54 simultaneouschannel pairs for a single MDBS. Further expansion to the CDPD channelcapacity is possible by covering the sectors (as defined by AMPS antennacoverage) with logically separate local mobile data base stations.However, such expansion could result in complications regarding theshared front end equipment necessary for transceiver operation (notshown in FIG. 4).

The chassis 30 of FIG. 3 is arranged to accommodate aSniffer/modem/transceiver board with two receive RF port connectors, anda sniffer port connector. This is used to connect the sniffer found onthe SNODEM boards to a place on the AMPS circuit appropriate fordetection of AMPS communications on selected new frequency channels.

The MDBS contains one fault contact closure pair associated with eachcontrol computer board slot. A fault contact pair closes when any fatalfault is detected by the control computer associated with the contactpair. Fatal failures include power failure, failure of the controlcomputer containing the contacts, or failure of allSniffer/modem/transceiver boards. If only one control computer isinstalled, the contact pair associated with the vacant control computerboard slot will be closed. If the MDBS is configured with two controlcomputer boards, the contacts can be wired in series, in parallel, orindividually monitored based on the desired resource managementphilosophy. If desired, the fault contact closures can be connected tothe host (AMPS cellular base station).

A more detailed representation of the Sniffer/modem/transceiver board 45is illustrated in FIG. 5. The Sniffer/modem/transceiver board 45 isdepicted as having a modem portion 51, for converting digital signals toanalog radio frequency signals and vise versa in order to transmitrepresentations of data processed in other parts of the system. SNODEMboard 45 also includes sniffer 52 connected to detect AMPScommunications. The radio receiver 53 and radio transmitter 54 are alsoincluded and are connected to the RF front end portion 50.

The front end portion 50 is expected to be shared with the normal AMPSbase station. For each Sniffer/modem/transceiver (SNODEM) board 45,additional front end equipment used for AMPS transmissions can beconnected to a respective SNODEM board as illustrated in FIG. 5. Thefront end equipment includes but is not limited to a directional coupler55 for permitting the sniffer 52 to detect activity on AMPS channelsused by other transceivers at the AMPS base station, and an attenuator63 used to provide the proper power level to the sniffer 52. Thepreamplifiers 58 and 58' feeding a splitter 56 are used to amplify weakincoming signals for detection by a number of SNODEM boards 45. Radiofrequency bandpass filters 59, and 59', are used as an aid to tuning theproper radio frequency signals. Power amplifier 57 is necessary to boththe CDPD and AMPS communication systems in order to provide signals ofsufficient strength to be received throughout the area covered by a basestation. The duplexers 60, 60' are used to allow the antennas 61 and 62to operate in more than one mode (transmit and receive).

Some installations employ three separate antennas per sector or cell,one for transmission and two for space diversity reception. Typically,signals from both antennas 61, 62 pass through the band pass filters 59,59', and preamplifiers 58, 58', and then are split into signals thatfeed each of the AMPS receivers. The antennas 61, 62 can also feedsignals to the CDPD receiver 53, as shown in FIG. 5. In installationssuch as that shown in FIG. 5, the RF front end portion 50 that must beprovided as part of the MDBS will consist of the sniffer coupler(directional coupler 55) a non-linear power amplifier 57 as well as theother equipment illustrated as part of front end portion 50.

It is also possible to use CDPD as an omni-directional channel systemoverlaying a sectorized AMPS cell site (not illustrated). In this case,a separate power amplifier must be used, and a non-linear amplifier(NLA) end receiver and bypass filter are also required since none ofthese items may be shared with the AMPS equipment. Such a system can beconfigured with two antennas using a duplexer or with three antennaswithout a duplexer. The sniffer must be driven by a signal formed bycombining the coupled outputs of all sectors at the site. Alternatively,channels can be dedicated to CDPD operation and the sniffer disabled.However, this is generally undesirable for the reasons mentioned supra.

Many AMPS cell sites use non-linear power amplifiers for the transmitterwith one amplifier per RF channel; in this case, each CDPD channel alsorequires its own power amplifier 57 as illustrated in FIG. 5. Theduplexers 60, 60' are used to provide isolation between the transmittedsignal and the receiver path. This results in a slight degradation tothe AMPS sensitivity because any duplexers are high loss devices.Typical signal attenuation due to the duplexers are approximately 0.7dB.

In the alternative, a linear power amplifier can be used, the CDPDchannels can be combined with the AMPS channels at low power levelsprior to amplification by the linear power amplifier. This arrangementeliminates the need for separate power amplifiers and duplexers andreduces costs considerably. Thus, any number of different arrangementscan be used for sharing front end equipment, so that FIG. 5 is not theonly arrangement possible or practical for use with the mobile data basestation of the present invention.

The arrangement of FIG. 5 can be altered by adding an additionalreceiver to the radio frequency portion of board 45 in FIG. 5. Thisadditional radio frequency receiver can be connected to splitter 56 in atwo-antenna arrangement, or can be connected to the third antenna (notshown), depending upon the specific characteristics required by thesystem operator. An antenna diversity scheme to optimize RF gain systemscan be effected by adding a third shared antenna for reception (notshown) and a switch for selecting antennas. It is noted that antennadiversity can be constituted by any number of different arrangements andis not limited to that presented so far in this application. However,there must be sufficient processor capacity to accommodate necessaryprogramming for switching between antennas.

Sniffer operation varies slightly depending on the front end arrangementused. The sniffer 52 samples the RF energy on channels coupled from theAMPS transmit path, and allows CDPD transmission only on inactive AMPSchannels. While the network is in operation, the sniffer continues tomonitor both the channel in which the CDPD is active and other candidatechannels for AMPS activity. If an AMPS connection is established on thechannel that the CDPD system is using, the sniffer will rapidly detectthe event, and the MDBS will hop to another unoccupied AMPS channel.

Subscribers (M-ES) are notified in advance of the channel that the MDBSplans to hop to (based upon a method disclosed infra), and when the M-ESdetects the loss of the forward link (communications received from theMDBS), they also hop to the new channel. The channel hop andreacquisition occur rapidly enough so that there is no noticeabledegradation in either AMPS service or CDPD service. Reverse link datapackets (originating at the mobile end systems 2 as illustrated inFIG. 1) may be temporarily dropped as a result of channel hops, buthigher level link protocols result in the retransmission and recovery ofany data lost through such hops.

In the arrangement (using a non-linear power amplifier) where the AMPSand CDPD are not combined prior to sniffing because the CDPD signal istransmitted via one of the AMPS receive antennas, the sniffer needs onlyto differentiate between the presence and absence of a signal on thetransmit antenna, and because the power level when AMPS transmissionbegins is very large (more than 50 dB), the sniffer can act very quicklyto cause CDPD transmissions to cease once AMPS transmissions aredetected.

In a configuration using linear power amplifiers, the combined CDPD andAMPS signals appearing at the output of the AMPS power amplifier iscoupled to the sniffer. Since the sniffer must detect only a smallincrease in the power on the channel resulting from the addition of theAMPS signal (typically 3 dB), it takes somewhat longer to determine whenan AMPS transmission has started on a channel already occupied by CDPD.However, determining which channels are vacant takes no longer than inthe case of non-linear power amplifiers.

The sniffer's determination of collisions is still made within the 40millisecond window required by the CDPD system specification, providedthat the AMPS signal power level is no less than 2 dB below the CDPDsignal power. This is the case in existing systems which are designedwith no forward power control (power is set to a level adequate toprovide coverage to the entire sector for all connections, which is alsothe case for CDPD) and those that do have forward power control but usefull power until the connection is established and then are powereddown.

In some cases, the sniffer can be eliminated from the transceiver modemcard if the AMPS equipment can provide a signal indicating AMPSactivity. In this case, a serial port connection is established toexchange AMPS and CDPD channel activity information. Use of thisconfiguration can result in a cost savings since the SNODEM boards maybe provided without the sniffer. In this configuration, three antennasare preferable as part of the front end portion I, although only two canbe used. The radio receivers 53 and radio transmitter 54 illustrated inFIG. 5 are essentially the same as those used for AMPS equipment in anassociated AMPS base station. However, the modulation/demodulation(modem) and control portions of the SNODEM board 45, are specificallyconfigured to provide a compact and modular MDBS for optimallytransmitting and receiving CDPD signals using existing AMPS equipment.These attributes result from a division of functionality on both theSNODEM board and the control computer board.

The modem portion 51 of the SNODEM board 45 (FIG. 5) is responsible forall CDPD digital signal processing including GMSK (Gaussian minimumshift keying) modulation and demodulation, Reed-Solomon Error CorrectionCoding and Decoding, and other airlink data processing.

The radio transceiver portion 53, 54 performs frequency up-conversionand down-conversation to and from RF channels within the cellular bandcommanded by the control computer 44 (in FIG. 4). A synthesizer withinthe radio transceiver portion provides all required frequencies forthese conversions. The transmitter output can drive most standard singlechannel AMPS cellular base station power amplifiers, but in the case oflinear power AMPS it also includes a power level control circuit toallow the interface to adjust the power output by adjusting the poweramplifier's drive level. The transmitter output signal is normallyturned on or off under microprocessor control, but there is also afront-panel toggle switch (not shown in casing 30 in FIG. 3) whichallows the output stage of the transmitter to be directly disabled. Thereceiver section of the radio transceiver preferably contains twocomplete down-conversion paths to support antenna diversity with signalcombining. This provides significant performance improvement overnon-diversity configurations, especially when receiving signals frommoving mobile end system.

The SNODEM board is designed to transmit on the backplane 42 (in FIG. 4)only during an assigned time slot, and only if it has received a messagefrom the control computer 44 (in FIG. 4). The SNODEM board also receivesa health and status pole from the control computer 44 at least one persecond. The control computer board cannot directly force a SNODEM boardinto a reset state. Consequently, it is up to the SNODEM board to make adetermination and reset itself if appropriate upon detecting an internalfailure. For example, the SNODEM board will reset if it stops receivinghealth and status poles from the control computer or if there is anindication that the queue of available optimum channels for CDPDtransmission is blocked.

As previously indicated, each SNODEM board has a sniffer RF portconnector located on its front panel. The connector type is SNA. Theimpedance of this port is 50 ohms with VSWR of not more than 1.5:1, andthe impedance must be 50 ohms with a VSWR of 1.5:1 for proper operation.The sniffer can reliably detect the presence of an AMPS signal when thesignal on the channel being measured has a power level in the range of-22 to -53 dBm at the sniffer RF port. The signal may be only an AMPSwave form, only a CDPD wave form, or summation of AMPS and CDPD. Thesniffer will reliably detect AMPS combined with CDPD if the AMPS signalis no more than 2 dB smaller in power level than the CDPD signal. TheMDBS will detect the onset of an AMPS signal (where onset is a time atwhich the AMPS signal attains a power level as described above) on thechannel used by CDPD and will cease to transmit (i.e., the power levelthe MDBS transmitter port will be -70 dBc) on this channel within 40milliseconds with probability of 99.9%.

FIG. 6 illustrates the elements contained in the modem portion 51 (FIG.5) of the SNODEM board 45 In order to facilitate the division offunctionality between separate boards (such as the SNODEM board and thecontrol computer board), functionality is also specifically dividedbetween the various elements on each board. The control processor 601for the SNODEM is constituted in a preferred embodiment by a MotorolaM68302 chip. This chip also functions as an input/output processorconnecting the SNODEM to a utility port 605 and the backplane 42. Thecontroller 601 is responsible for the following functions necessary forthe operation of the MDBS:

1. maintaining an RF channel list for CDPD communication;

2. system start-up;

3. downloading code (from the control computer board 44 to the othercomponents on the SNODEM board);

4. reporting the status of SNODEM board to the control computer board44;

5. processing incoming and outgoing data packets including applyingprimitives of protocols conducted between the MDBS and external elementssuch as the MD-IS and the NMS;

6. processing serial and DPRAM interface commands;

7. scanning RF channels;

8. indicating presence of voice communication on CDPD channels;

9. indication of change of status in channels;

10. performing channel hopping;

11. routing packet types between the backplane and the digital signalprocessor;

12. frame flag insertion;

13. general message routing and maintenance of message routing queues;

14. generation and routing of channel queues to the control computerboard.

The SNODEM board also contains two digital signal processors 602,603each preferably constituted by a Texas Instruments TI320C51 chip. Thefirst digital signal processor (DSP1) 602 carries out the followingfunction:

1. converting signals to CDPD block format, and carrying out the reverseof this process;

2. carrying out a dotting sequence to detect the start of a burst ofsignals constituted by digital 1's and 0's; and

3. feeding samples to an analog digital converter on the sametransceiver card.

The second digital signal processor (DSP2) 603 carries out the followingfunctions:

1. converting CDPD blocks to a frame format, and reversing this process;and

2. carrying out error correction, preferably Reed/Solomon encoding.

It is noted that the second DSP function is primarily an auxiliary tothe first DSP and can be replaced if the first DSP is constituted by afaster processor with more memory.

Utility port 605 permits a CDPD operator to carry out hardware/softwarediagnostic and repair activities. To access the system, the operatorwill be required to log on and enter a password correctly. CDPD softwaredescribed in Appendices VI, X and XIII of this application will supportoperator entry of the following commands:

1. initiate CDPD operation (i.e., transmit forward channels, receive andprocess reverse channels);

2. add and delete CDPD logical channels;

3. terminate CDPD operations (i.e., cease transmission of forwardchannels and process of reverse channels);

4. display current MDBS equipment status;

5. display current analog activity (i.e., RF sniffing data);

6. display event/alarm log containing the last entries;

7. monitor system operation;

8. display/edit MDBS data base;

9. command diagnostic execution; and

10. exit CDPD software and return to operating system prompt.

Also included are two XILINX field programmable gate arrays (FPGA)604,608. These are relatively simple processors in terms of functions ascompared 601, 602 and 603. However, each XILINX array has a relativelyhigh number of input/output ports as compared to the other processors onthe SNODEM. Consequently, the XILINX arrays facilitate certainoperations necessary in the MDBS using a minimum of physical space andprocessor capacity. The first XILINX array 604 is operatively connectedto the backplane and processor 601 (as well as SRAM 606, EPROM 607 andXILINX 608). This array carries out the following functions:

1. interface with the backplane 42;

2. hardware polling; and

3. generation of slot designation signals. The second XILINX array 608functions as a digital-to-analog (D-A) converter and as a A-D converter.This converter is configured so that digital filtering is carried out.This XILINX array also carries out signal division to provide signalsfor the phase lock loops required on the SNODEM board.

The second XILINX array 608 is configured to carry out delta-sigmamodulation thus eliminating more elaborate and space-consumingcircuitry. The elements including in this configuration are illustratedin FIG. 7, and are entirely contained within the second XILINX array 608(with the exception of the lowpass filter 707).

The delta-sigma technique can be very useful in most applications forsample rates below 100 kHz and may have significant applicability athigher rates. The delta-sigma approach for CDPD communication allowsreplacement of standard DAC and a four or five pole anti-alias filterusing a simple accumulator and a two-pole lowpass filter in thisparticular application.

The object of the circuit illustrated in FIG. 7 is to put the noiseassociated with the sampling of an input signal in Gaussian terms andthen spreading the power spectrum of the noise signal so that a majorpart of the noise waveform can be eliminated using a simple low passfilter. The circuit in FIG. 7 carries out the necessary manipulation toallow the two-pole low pass filter 707 to eliminate the majority of thequantized noise associated with signal sampling due to the spreading anda shaping of the noise wave form into a Gaussian-like signal which canbe shifted, and to a large extent eliminated. As illustrated by FIG. 7,a digital signal Sk is input to register 701. Sampling of this signal iscontrolled by an eight bit counter 702 to produce a 8-bit output to besent to adder 703. The input frequency of 4.9152 MHz to the 8-bitcounter 702 is generated on the SNODEM board and is divided by 64 tocontrol register 701. Another frequency division is carried out in the8-bit counter 702 to produce an output of 19.2 kHz which is used inanother part of the SNODEM board. The original frequency of 4.9152 MHzis used to control register 704 which receives the output of adder 703.As a result, register 704 samples at a much higher rate than register701 and sends back its output signal to combiner 703. The result is acarry signal (output signal) more closely approximating an analog signaldue to the high sampling rate of register 704. This output is fed to a Dflip-flop 705 which cleans up glitches created in the carry circuit byother circuit components. Limiter 706 assures that the level of theoutput stay constant and remains in a form translatable to an analogsignal. The output of limiter 706 results in a signal St swinging from+V to -V absent a substantial portion of the noise resulting from thesampling carried out in register 701 by bit counter 702. Using thisconfiguration, the DAC and ADC circuitry (except for the lowpass filter707) is contained in one XILINX array, thus, eliminating the need forthe substantial space required by conventional DAC and ADC devices. As aresult, the entire circuitry necessary can be maintained within theSNODEM board effecting the necessary modularity within the MDBS.

The other elements illustrated in FIG. 6 cooperate with theaforementioned digital signal processors and XILINX arrays. SRAM 606 isused to hold an operational code. EPROM 607 permits additional functionsby the I/O processor 601. The DPRAM 609 is used as a buffer for allcommunication between the first digital signal processor 602 and the I/Oprocessor 601. EPROM 610 serves the same function between the first andsecond digital signal processors 602, 603. The two digital signalprocessors 602, 603 use SRAM 611, 612, respectively for holding andbuffering information.

Optimum channels for CDPD communication are based on queues of theoptimum channels for AMPS communications. However, future channelsdedicated to CDPD use may become available. With CDPD communicationthose channels selected for optimum use are those channels which areleast likely to be used in AMPS communications and thus, correspond tothose channels at the bottom of the AMPS queues. The list (queue) ofchannels to be considered for CDPD use is derived in much the samefashion as those used for AMPS use. In both cases, communicationschannels are divided into two areas based upon traditional use. Thefirst area is the original RF channel spectrum allocated for cellularcommunication and the second area is based upon the extended RF channelspectrum developed after the original allocation for radio telephonecommunication was made. The most heavily used (by AMPS) group ofchannels is in the extended spectrum since this area is allocated firstin order to reserve the original spectrum for those systems which do nothave the capacity to use the extended spectrum. As a result there willbe two queues. One used for the original spectrum and one for theextended spectrum.

The CDPD system of the present invention will use these two queues inmuch the same way except that the last used AMPS channel will always beat the bottom of the AMPS queue while the same channel will always be atthe top of the CDPD queue since it is a channel least likely to be usedin AMPS communication. This is done for both the extended spectrum areaand the traditional spectrum areas. Since the traditional spectrum areais least likely to be used for AMPS communication because of theassignment in priority to the extended spectrum, the traditionalspectrum will have the highest priority for CDPD usage. If AMPS systemis limited to the traditional spectrum, and a CDPD mobile data basestation having capability in the extended spectrum is adjoined thereto,then the most likely channels for CDPD use would be found in theextended spectrum rather than the traditional spectrum.

In a variation of the original arrangement each of the spectrums can bedivided into two lists of channels. The first in each spectrumdesignated as A and the second designated as B. One of these lists canbe given priority over the other based upon any number of factorsdetermined by the system operators. The priority of the lists can bechanged from A to B periodically, for example, every half hour, in orderto offset overuse of the high priority group.

The logical algorithms used for channel assignment can be selected forthe best possible compatibility with the different types of AMPS channelassignment strategies to minimize potential for collisions, and also toavoid conflicts with "sealing techniques employed by some AMPSequipment". "Sealing", sometimes called "foreign carrier detection", isa technique used in some AMPS cell site equipment in which unusedchannels are probed for the presence of RF energy, and, if energy ispresent, are "sealed" from AMPS usage until the energy goes away. CDPDsignals appear to AMPS as a foreign carrier and would result in theeffected channel being sealed. Thus, in a cell site with sealingcapability, if CDPD dwells on a channel long enough to trigger sealing,it will end up degrading AMPS capability because the AMPS system willavoid using that channel until the CDPD communication hops to anotherchannel.

Now referring to FIG. 6, the backplane 42 is used to communicate betweenthe control computer board (S) 44, 44' (in FIG. 4) and the SNODEM boards45, as well as the power supply boards illustrated in FIG. 3. Thebackplane consists of two independent serial interfaces that allowcommunication to all the MDBS cards. The backplane carries the followingsignals:

1. a 1.4 MHz clock;

2. signals indicating the start of a new time slot (SNODEM boards onlybeing allowed to transmit during their assigned slot);

3. serial data driven by any board that has data to send during itsassigned time slot; and

4. identity bits providing the backplane bus slot identity for eachindividual board. Only one backplane is active at any instant. Themaster control computer 44 (in FIG. 4) determines which backplane to useand when to switch to the second backplane in the event of a fault.Faults of the backplane include loss of clock, loss of data stream, lossof protocol slot timing information and jammed data bus due to a faultycontinuous transmission. The backplane is also crucial to the selectionof a master control computer board 44 if more than two control computerboards are used in the MDBS. The backplane is also necessary forredundant operation of certain MDBS elements in the event of faultdetection.

Each board in the MDBS contains one contact closure pair associated witheach control computer slot. A fault contact pair closes when any fatalfault is detected by the control computer associated with the contactpair. Fatal failures include power failure, failure of the controlcomputer containing the contacts, or failure of all SNODEM boards. Ifonly one control computer is installed, the contacted pair associatedwith the vacant control computer slot will be closed. If the MDBS isconfigured with two control computers, the contacts can be wired inseries, in parallel, or individually monitored based on the desiredresource management philosophy. If desired, the fault contact closurescan be connected to the host cellular base station.

Redundant operation is especially critical with respect to the powersupply modules. Each one of these slides into one of two power supplyslots at the front of the casing 30 (in FIG. 3). Each power supplymodule accepts 24 VDC from the main DC power bus available at cell sitebase stations and generates the voltage forms needed for operation ofMDBS modules. The power supply board also provides power conditioning toreduce the effects of noise and a voltage variation on the main batteryline, and controls the sequencing of the voltage forms during powerturn-on as required by the MDBS boards. Redundancy can be provided forimproved reliability, with a hot switch capability that allowsuninterrupted operation through single point failures.

During normal operation the power supplies share the load. If one powersupply fails, the other power supply takes over the entire loadfollowing one of a number of different methods well known in the art ofproviding uninterrupted power. Each power supply board has two statuslines that are periodically read by the control computer. The first lineis an over voltage status line and the second is an under voltage statusline. In addition, there are two control lines that can be asserted bythe control computer in the event of a power supply fault, i.e., overvoltage, under voltage or over current conditions. Under normalconditions, the control computer cannot assert control over the powersupply via these two control lines. After these control inputs areenabled, the control computer can turn off the power supply at any time,regardless of the internal power supply conditions.

The MDBS is designed to cover single point failures. In general, this isaccomplished by switching in a redundant component without managementintervention. The minimum fully redundant configuration for a cellsector supporting a single CDPD channel consists of two controlcomputers, two SNODEM board and two power supply boards.

FIG. 8 illustrates the elements arranged on the control computer board44. The control processor 803 of the control computer board ispreferably constituted by an advanced micro devices (AMD) 29200 chip.This chip carries out the following functions:

1. periodically polling all other boards for help or status information;

2. reporting alarm, health and status information to the networkmanagement system (NMS) through the network port 810 using a DS0 line;

3. radio resource management and generation of commands to the SNODEMboards;

4. generation and distribution of master clock timing; and

5. downloading software to all other boards in the MDBS (if the controlcomputer board is the master control computer board).

If more than one control computer board is utilized in an MDBS, adesignation of the master control computer board is made by default onthe basis of the slot into which the control computer board is placed.The control computer board designated as the master downloads externalinstructions to all other boards in the MDBS. The master controlcomputer board can also serve as a master for other MDBS chassis.Additional slave computer control boards can be added for more channelsor faster processing. Those control computer boards not designated as amaster have a peer-to-peer relationship. The master control computer isparticularly important for distributing information to the other controlcomputers and other SNODEM boards in the MDBS by such instructions thatare received from an external source such as the NMS.

In case of massive software loss (except for the boot code which isstored in EPROM 607 on the SNODEM boards), software code can bedownloaded from external sources such as the NMS into the controlcomputer board. This download is made over a DS0 line connected toutility network port 810 (FIG. 8) connected to input/output processor801 using high-level data link control (HDLC) protocol. Software can bedownloaded through the network port 810 or the utility port 811 to thecontrol processor 803 and must pass through input/output processor 801.This process can be carried out when software disruption occurs or whenthe system is reprogrammed. During the process, the MDBS is shut downuntil the new software is loaded into the control computer board. If thereprogramming is prearranged and fails to work, the control computerboard can fall back on the old programming still retained in hard drive808 (FIG. 8).

Upon determining the acceptability of new software, the control computerboard downloads appropriate software to the other boards contained inthe MDBS. If reprogramming cannot be accomplished over the DS0 line tothe network port 810, a utility port 811 can be used to permit aprogrammer to input new software at the site of the MDBS. Only the bootcode is needed for an operator to carry out this process. This processis used only as a backup should the programming over the DS0 line failsince reprogramming each MDBS using the utility port is a tedious andtime consuming process.

Preferably, the reprogramming is conducted from a network managementsystem (NMS 10 in FIG. 1), as is maintenance, monitoring and adjustmentof each MDBS throughout the CDPD system. This is accomplished by meansof a special protocol conveying information between the NMS and theMDBS, preferably transparent to all other parts of the CDPD systemtherebetween.

The control computer board input/output processor 801 (FIG. 8) ispreferably a Motorola M68302 chip, connected to SRAM 802 and XILINX FPGAarray 809, as well as network port 810, utility port 811, dual port RAM(DRAM) 804 and backplane 42. This array carries out the followingfunctions:

1. system start-up and related system functions;

2. serial backplane bus communication;

3. utility port communication;

4. DS0 port communication;

5. packet data transfer;

6. debug monitoring;

7. sorting and routing of data into predetermined queues;

8. placement of CDPD frame headers; and,

9. inserting frame flags for identification and transmission on DS0channel.

There is also a XILINX array 809 operatively coupled to both thebackplane and I/O processor 801. Like the XILINX array 604 (in FIG. 6)on the SNODEM board, this XILINX array carries out the followingfunctions:

1. interfacing with the backplane board;

2. hardware polling; and

3. generation of slot designation signals.

In FIG. 8, communication between the control processor 803 and the I/Oprocessor 801 is carried out by a dual port RAM (DPRAM) 804. The controlprocessor 803 is enhanced by SRAM 806 for the purposes of carrying outmanagement functions. Operational codes are executed out of DRAM 807.The majority of the files necessary for the operation of the MDBS arecontained in the Hewlett Packard Kitty Hawk hard drive 808.

The control computer board 44 (FIG. 4) communicates with the SNODEMboard 45 over backplane 42. The control computer board transmits CDPDframes, radio resource management commands, SNODEM control commands, andnetwork management system queries to the SNODEM board 45. In return,each SNODEM board 45 sends CDPD frames, sniffer data, SNODEM statussignals and network management system (NMS) information to the controlcomputer board 44. Within the control computer board 44, theinput/output processor 801 (FIG. 8) communicates with backplane 42 aswell as the network port 810 over a DS0 line. The input/output processor801 communicates with the control processor 803 by sending CDPD frames,sniffer data, SNODEM status signals and NMS information to the controlprocessor 803. In return, the control processor sends CDPD frames, radioresource management commands, SNODEM control signals and NMS queries tothe input/output processor 801. The network port 810 handles incomingCDPD frames, adjacent MDBS channel status and NMS queries and commands.The MDBS sends CDPD frames, CDPD channel status and NMS information overthe DS0 link through network port 810.

Within the SNODEM board 45 the input/output processor 601 (FIG. 6) sendsCDPD frames, radio resource management commands, SNODEM control commandsand NMS queries to the two digital signal processors 602, 603. These inturn communicate CDPD data to the radio receiver 53, radio transmitter54 and RF front-end 50 which in turn conveys the CDPD data over theairlink to mobile end systems such as M-ES 2 (FIG. 1). Referring to FIG.6 the two digital signal processors sends CDPD frames, sniffer data,SNODEM status signals and NMS information (in response to queries) tothe input/output processor 601. In turn, this processor sends theappropriate signals to the control computer board 44 as previouslystated.

To fully utilize the CDPD system, a network management system (NMS) isnecessary. The NMS preferably monitors and directs the CDPD system at alocation remote from the mobile data base stations, downloading newprogramming when appropriate. The network management system (NMS) hasthe capability of downloading software into any MDBS in the CDPD systemvia a network link using a special mobile data base station utilityprotocol (MUP). This protocol is carried out in addition to the physicallayer, medium access control (MAC) layer and data link layer normallyused by the MDBS according to layered communications architecturestandard OSIL (Open system Inter connection).

The network management system (NMS) is concerned with the management ofthe various open system interconnection (OSI) elements used forestablishing, monitoring and controlling communications between thevarious system entities. The services provided include:

1. Names and addresses of users;

2. Determination of adequate resources and authority to communicate;

3. Quality of service to be provided; and

4. Agreement on the protocols for exchanging data.

The MDBS utility protocol (MUP) is a proprietary protocol which allowsconfiguration, control and debug functions to be performed on the MDBSlocally and remotely. This protocol will be used extensively in theinitial phase of the MDBS software deployment to provide control accessto the MDBS while a full feature network management system is not yetavailable. The MUP is capable of communicating with the MDBS via varioustransport and sub-network layers. In particular, the MUP will be carriedout over a DS0 link using a network port 810, and over an RS-232asynchronous link using the utility port 811 (FIG. 8). The MUP permits a"gateway" capability by which the MDBS network management software willaccess the MDBS utility software to provide utility functions. This isan alternate solution to the managing protocol for the MDBS described inSection 7.5 of the CDPD specification.

The MUP is a peer-to-peer protocol operating in an asynchronous balancedmode. Thus, all messages can be initiated at either the MDBS or the NMSsince both ends are generally considered as DTE's (data terminationequipment) in this particular implementation. This protocol supportsfull duplex communication as well as message "pipelining". A maximum ofthree outstanding unacknowledged send messages is permitted in thisimplementation.

The MUP is a byte-oriented protocol (meaning that the byte alignmentbetween protocol data is guaranteed at the physical layer). It isassumed in this protocol that only an integral number of bytes iscontained in the information field. This protocol requires that allframes start and end with a flag character (0×7E). This frame formatconsists of the aforementioned flag, an 8-bit address, an 8-bit controlportion, an information portion having from 0 to 256 bytes, the first8-bit frame check portion, a second 8-bit frame check portion and asecond flag.

The 8-bit address field is divided into two subfields: protocolidentifier (PID) and address. Bits 0-3 of this field are designated asthe protocol identifier field which is used to provide the protocolcompatibility check and allow the data link layer to support multipledata protocols. Bits 4-7 of this field is the device address field whichis used to provide multiplexing capability so that the MUP controllercan address its packet to either the primary or secondary controlcomputer within an MDBS.

As illustrated in FIG. 10, the MUP controller 1001, connected preferablyto the network management system for the CDPD system, initiates controlsignals or instructions to be received by the MDBS 1. These instructionsare output over a communication port 1002 and transmitted to mobile dataintermediate system (MD-IS) 1004 by means of an LAN/WAN or asyncconnection (RS-232) 1003. The MD-IS is expected to provide the necessaryinternet protocol (IP) routing functions (by means of IP router 1006) todirect the data package between the MUP controller 1001 and the MDBS 1.It is noted that in a LAN environment, both the MD-IS and the MUPcontroller are co-located as nodes on an Ethernet network and the MDBSis connected to the MD-IS via the DS0 link 1008. In a WAN environment,the MUP controller 1001 can be connected to the MD-IS 1004 via a WANnetwork such as X.25. If an async configuration is used, the MUPcontroller 1001 is connected to the MD-IS 1004 via an RS-232asynchronous serial connection. This can either be local or accessed viaa remote dial-up.

The MUP controller 1001 is configured as a DTE and the data format usedis: 1 start bit, 8 data bits, 1 stop bit and no parity. The baud ratesupported include: 1200 bps, 2400 bps, 4800 bps, 9600 bps, 19,200 bpsand 38.4 Kbps. However, high data rates may be available for internalengineering usage and the remote dial-up link may only support up to9600 bps. As a DTE device, the MUP controller 1001 will always assertthe RTS and DTR modem control signals when it is on line and it expectsto be presented with the appropriate DCE modem signaling (i.e., CTS, DCDand DSR should be asserted for proper communication).

In the local configuration, the MUP controller will be co-located withthe MD-IS on an Ethernet LAN. The MDIS is responsible for providing IProuting capabilities for the data traffic between the MDBS 1 and the MUPcontroller 1001. Thus, network programming is provided from a networkmanagement system (NMS) to mobile data base stations throughout the CDPDsystem. Using this arrangement, it is possible to reprogram all themobile data base stations through the master control computer board (ifa master board exists) in each of the mobile data base stations.Likewise if a master control computer board is used for a plurality ofmobile data base stations linked together, reprogramming of all of themobile data base stations (each of the SNODEM boards) is carried out bydownloading the programming to the master computer control board, andthen downloading at the command of the master computer control board tothe other portions of the mobile data base stations.

FIG. 9 illustrates a more detailed flow diagram correlating the dataprotocols to particular portions of the CDPD system. This figure furtherillustrates the occurrence of the MUP commands within the context of theoverall data flow. Beginning in the reverse directions (communicationsbeginning at the M-ES), a message from the mobile end system is arrangedin mobile data link protocol (MDLP) arranged in protocol data units(PDU). The message is framed and blocked (901) and run through thedigital sense multiple access protocol to arbitrate access to thereverse channel stream between more than one M-ES at the mobile accesscontrol layer 902. This data then is transmitted into the RF channelstream 903 and received by the MDBS transceiver unit (not shown). Thedigital signal processors at 904 carry out the reverse of the mapprotocol used at 902. The reverse of the blocking and framing is carriedout at 905 and the emergent instruction protocol such as a utilityprotocol MUP is transferred to the SNODEM I/O processor at 906. This MUPinstruction data (or response data if received from the M-ES) is giventhe headers appropriate to the MUP protocol which allows data be routedthroughout the internal CDPD system since the data packet is identifiedas to its contents and its source. The data is then routed by high-leveldata link control (HDLC) 907 through the backplane interfaced with theSNODEM board 908, through the backplane itself and into the backplaneinterface with the control computer board (at the I/O processor of thecontrol computer board) 909. The HDLC format is decoded at 910 allowingthe data MUP encapsulated by the MUP protocol to emerge 911.

The control processor of the control computer board will operate inresponse to MUP encapsulated instructions received or other externalsource such as the NMS over the utility port. The control processor willalso be cognizant of MUP encapsulated data generated by the SNODEMboard. Since the MUP encapsulated data is to be further transferred, itis operated on to produce MDLP protocol data units which are then actedon using data link layer protocol 912 in the control computer board I/Oprocessor. Data is then configured for the DS0 link which carries thedata from the MDBS 1 to mobile data intermediate system MD-IS 3 which isalso connected to the DS0 line at portion 914. Other data isreconfigured for the data link layer 915 and emerges as MDLP protocoldata units shown in FIG. 9 at the MD-IS. Because the MDBS utilityprotocol (MUP) identifies the nature of the data packet and its source,it can be used throughout the system to convey instructions on any partof the system such as the NMS to any of the mobile data base stations.

A major advantage of the present invention is that the CDPD mobile database station can be provided at a normal AMPS base station with aminimum of space and no impact upon the AMPS system. The presentinvention is highly flexible due to its modular design in which grossfunctions of the MDBS are divided by means of separate boards stridablymountable in the MDBS casing. This flexibility is further facilitated byfurther sub-divisions of functionality amongst the elements found on theboards constituting the MDBS. The efficiency of the CDPD system isenhanced by a novel channel hopping scheme, and each MDBS in the CDPDsystem can be remotely programmed from a network management system forthe entire CDPD system using a unique protocol to exchange data betweenthe NMS and MDBS. Since size is critical in the layout of the MDBS, theuse of a normal DAC or ADC devices is eliminated through the use ofdelta-sigma modulation. Because of the compactness and flexibility ofthe MDBS, it is easily arranged to share front-end equipment (such asduplexers, power amplifiers, splitters and antennas) with existing AMPSinstallations.

Although a number of arrangements of the present invention have beenmentioned by way of example, it is not intended that the invention belimited thereto. For example, the present invention can be adapted withthe appropriate use of utility ports and DS0 links to interconnect aplurality of mobile data base stations, all under the control of asingle master control computer board. Accordingly, this invention shouldbe considered to include any and all configurations, modifications,variations, combinations or equivalent arrangements falling within thescope of the following claims.

What is claimed is:
 1. A mobile data base station (MDBS) configured totransfer cellular digital packet data (CPDP) between at least one mobileend system (M-ES) and a mobile data intermediate service (MD-IS), saidMDBS comprising:a controller board operatively connected to said MD-ISvia a data link and arranged to receive and convey operatinginstructions; a transceiver board providing a radio link to said atleast one M-ES and arranged to operate based on instructions receivedfrom said controller board, said transceiver board being separate anddistinct from said controller board; said MDBS is collocated with amobile phone system station; said controller board and said transceiverboard are operatively interconnected through a backplane; at least onepower supply board is operatively connected to supply power to saidcontroller board and said transceiver board through said backplane;wherein said power supply board comprises means for detecting powerabnormalities throughout said power supply board, said backplane, saidcontroller board and said transceiver board; a chassis, in which saidcontroller board, said transceiver board and said power board areslidably mounted in a vertical position, and including a plurality ofdistinct mounting positions for said controller board, said transceiverboard and said power supply board; wherein said chassis includesdistinct mounting positions for a plurality of controller boards, aplurality of transceiver boards and a plurality of power supply boards;a second power supply board, said second power supply board operates inresponse to said means for detecting power abnormalities to operate in aredundant manner sharing load from said controller board and thetransceiver board; and wherein said power supply boards operate in aredundant manner responsive to at least one said controller board. 2.The MDBS of claim 1, wherein said controller board comprises a controlprocessor programmed for radio resource management and generation ofcontrol commands to said transceiver board and an input/output (I/O)processor programmed for routing data throughout said MDBS, said controlprocessor and said I/O processor being operatively connected to eachother.
 3. The MDBS of claim 2, wherein said control processor isoperatively connected to said data link through said I/O processor, andsaid I/O processor is also operatively connected to said backplane. 4.The MDBS of claim 3, wherein said data link is a class zero dataswitching (DS0) channel.
 5. The MDBS of claim 3, wherein said I/Oprocessor is operatively connected to said backplane using a high leveldata link control (HDLC) protocol.
 6. The MDBS of claim 2, wherein saidI/O processor is operatively connected to a first utility port.
 7. TheMDBS of claim 6, wherein said I/O processor comprises means forreceiving program instructions through said first utility port.
 8. TheMDBS of claim 4, wherein said I/O processor comprises means forreceiving program instructions through said data link.
 9. The MDBS ofclaim 5, wherein said controller board further comprises a dual portrandom access memory (DPRAM) operatively connected to and thatfacilitates communications between said control processor and said I/Oprocessor.
 10. The MDBS of claim 5, wherein said backplane comprisesmeans for transmitting data between a plurality of controller boards andtransceiver boards.
 11. The MDBS of claim 10, wherein said means fortransmitting comprises at least two HDLC protocol serial bus lines. 12.The MDBS of claim 1, further comprising connectors at each of saiddistinctive mounting positions, said connectors being arranged toprovide contact between respective boards and an HDLC serial bus on saidbackplane board, and each said connector having a predeterminedimpedance suitable for inserting a board in a respective mountingposition without creating power abnormalities.
 13. The MDBS of claim 1,further comprising a plurality of said controller boards, operativelyconnected through said backplane in a master/slave relationship betweenone of said controller boards and all remaining controller boards. 14.The MDBS of claim 13, wherein said slave controller boards operate in aredundant fashion to said master controller board.
 15. The MDBS of claim2, wherein said control processor comprises a circuit that selects achannel for CDPD communications.
 16. The MDBS of claim 15, wherein saidcontrol processor generates a health and status polling signal.
 17. TheMDBS of claim 16, wherein said health and status polling signal isgenerated at least once per second.
 18. The MDBS of claim 2, furthercomprising a plurality of front end equipment shared with said mobilephone system base station.
 19. The MDBS of claim 18, wherein each ofsaid plurality of front end equipment comprises a plurality of antennas.20. The MDBS of claim 19, comprising means for combining signals fromthe plurality of antennas.
 21. The MDBS of claim 20, wherein saidplurality of antennas comprises three antennas.
 22. The MDBS of claim21, further comprising a channel dedicated to CDPD communications. 23.The MDBS of claim 22, wherein said third antenna is dedicated to CDPDcommunications.
 24. The MDBS of claim 2, further comprising a pluralityof channels used for CDPD communications.
 25. The MDBS of claim 19,wherein each of said front end equipment further comprises duplexersoperatively connected to radio frequency amplifiers.
 26. The MDBS ofclaim 2, wherein said controller board and said transceiver boardcomprise means for carrying out a plurality of communication protocols.27. The MDBS of claim 26, wherein said communication protocols includephysical layer, medium access control layer, data link layer, and MDBSutility (MUP) and network layer.
 28. The MDBS of claim 26, wherein saidI/O processor further comprises means for developing a queue ofsuggested transfer channels based upon output signals from a sniffer.29. The MDBS of claim 26, wherein said queue information is transmittedfrom said MDBS to mobile subscribers on a periodic basis.
 30. A mobiledata base station (MDBS) configured to transfer cellular digital packetdata (CDPD) between at least one mobile end system (M-ES) and a mobiledata intermediate service (MD-IS), said MDBS comprising:a controllerboard operatively connected to said MD-IS via a data link and arrangedto receive and convey operating instructions; a transceiver boardproviding a radio link to said at least one subscriber M-BS and arrangedto operate based on instructions received from said controller board,said transceiver board being separate and distinct from said controllerboard; a plurality of power supply boards operatively connected tosupply power to said controller board and said transceiver board througha backplane; a chassis, in which said controller board, said transceiverboard and said power board are slidably mounted in a vertical position,and including a plurality of distinct mounting positions for saidcontroller board, said transceiver board and said plurality of powersupply boards; wherein said chassis includes distinct mounting positionsfor said controller board, said transceiver board and said plurality ofpower supply boards; wherein said plurality of power supply boardscomprises means for detecting power abnormalities throughout saidplurality of power supply boards, said backplane, said controller boardand said transceiver board; wherein said plurality of power supplyboards operate in response to said means for detecting powerabnormalities to operate in a redundant manner sharing load from saidcontroller board and said transceiver board; wherein said MDBS iscollocated with a mobile phone system base station; wherein saidcontroller board and said transceiver board are operativelyinterconnected through said backplane; and wherein said plurality ofpower supply boards operate in the redundant manner responsive to saidcontroller board.